The study involved before and after analysis of gene expression profiles in tissue samples taken from 25 healthy older men and women who underwent six months of twice weekly resistance training, compared to a similar analysis of tissue samples taken from younger healthy men and women.

The gene expression profiles involved age-specific mitochondrial function; mitochondria act as the "powerhouse" of cells. Multiple studies have suggested that mitochondrial dysfunction is involved in the loss of muscle mass and functional impairment commonly seen in older people.

Results showed that in the older adults, there was a decline in mitochondrial function with age. However, exercise resulted in a remarkable reversal of the genetic fingerprint back to levels similar to those seen in the younger adults. The study also measured muscle strength. Before exercise training, the older adults were 59% weaker than the younger adults, but after the training the strength of the older adults improved by about 50%, such that they were only 38% weaker than the young adults.

"We were very surprised by the results of the study," said Buck Institute faculty member Simon Melov, PhD. " The fact that their 'genetic fingerprints' so dramatically reversed course gives credence to the value of exercise, not only as a means of improving health, but of reversing the aging process itself, which is an additional incentive to exercise as you get older."

In a four month follow up after the study, most of the older adults were no longer doing formal exercise in a gym, but most were doing resistance exercises at home, lifting soup cans or using elastic bands. "They were still as strong, they still had the same muscle mass," said Mark Tarnopolsky, MD, PhD, of McMaster University Medical Center in Hamilton, Ontario. "This shows that it's never too late to start exercising and that you don't have to spend your life pumping iron in a gym to reap benefits."